1. Field of the Invention
This invention relates generally to armatures for high precision electric motors, and more particularly, to a motor shaft and method of preparing same for securing permanent rotor magnets thereto.
2. Description of the Related Art
High precision electric motors present difficulties in the attachment of permanent magnets that form the armature to the precision shafts. Usually, the shafts are finished with a smooth surface that will not permit adhesion of the permanent magnets. In addition, the precision shafts cannot tolerate conventional forms of surface preparation that would enhance the ability of the adhesive to form an effect of attachment. Any such surface preparation would change of the diameter of the shaft whereby it would be out of specification.
There is a need, therefore, for a method of preparing a shaft so that it can accept adhesion of the permanent magnets of the rotor without causing the diameter of the shaft to be out of predetermined tolerances.
A conventional precision motor shaft has a working portion and a rotor region. The working portion has a helical groove formed therein of multiple machining passes. Each such machining pass deepens the helical groove. In such known precision permanent magnet motors, the rotor region remains smoothly finished, causing the aforementioned difficulties in achieving adequate adhesion of the permanent magnets.
It is, therefore, an object of this invention to provide a shaft for a precision permanent magnet motor, the shaft having a rotor region that is finished to accept adhesion of permanent magnet motors, without the diameter of the shaft of being changed.
It is another object of this invention to provide a method of forming a shaft for a precision permanent magnet motor wherein the shaft is provided with a helical groove in a working region thereof, and a rotor region is simultaneously configured to enhance adhesion of permanent magnets.
The foregoing and other objects are achieved by this invention which provides, in a first method aspect thereof, a method of forming a precision shaft for a permanent magnet motor. This first method aspect of the invention includes the steps of:
first defining a working region of the precision shaft having an associated working surface region;
second defining a rotor region of the precision shaft having an associated rotor surface region, the rotor region of the precision shaft having a first predetermined cross-sectional diameter;
first preparing the working surface region of the precision shaft using a cutting tool, the step of first preparing including the further step of performing a first cutting pass by the cutting tool;
second preparing the rotor surface region of the precision shaft using the cutting tool, the step of second preparing including the step of continuing the first cutting pass by the cutting tool into the rotor surface region of the precision shaft; and
third preparing the working region of the precision shaft using the cutting tool, the step of third preparing including at least a second cutting pass by the cutting tool into the working surface region of the precision shaft, wherein the steps of first preparing the working surface region of the precision shaft and second preparing the rotor surface region of the precision shaft include the step of forming a continuous helical cut along the working and rotor surface regions of the precision shaft, whereby an inter-helix region of the rotor surface region of the precision shaft retains the first predetermined cross-sectional diameter.
In a specific illustrative embodiment of this method aspect of the invention, there is provided the further step of forming a continuous helical cut along the working and rotor surface regions of the precision shaft is performed at a depth of approximately between 0.001xe2x80x3 and 0.004xe2x80x3 into the rotor surface region. Preferably, the continuous helical cut along the working and rotor surface regions of the precision shaft is performed at a depth of approximately 0.003xe2x80x3 into the rotor surface region. The step of forming a continuous helical cut along the working and rotor surface regions of the precision shaft, in this specific illustrative embodiment of the invention, is performed using a cutting tool having a radius of approximately 0.020xe2x80x3.
Once the continuous helical cut along the working and rotor surface regions of the precision shaft, there may be provided a plurality of further continuous helical cuts, in the form of machining passes, only in the working surface region of the precision shaft.
In this specific illustrative embodiment of the invention, once the working surface region has been cut to form the desired depth of continuous helical cut, there is further provided the step of installing a permanent magnet onto the rotor surface region of the precision shaft. This step can be performed using epoxy as an adhesive. In a highly advantageous embodiment, the epoxy is an A+B heat cured type of epoxy, and preferably conforms to specification MMM-A-132.
In accordance with an apparatus aspect of the invention, there is provided a rotor for a permanent magnet motor, the motor having a rotor. In accordance with the invention, the rotor has a rotor shaft that is provided with a working region for delivering mechanical energy, and a rotor region that is arranged coaxially with the working region, the rotor region having a rotor region surface having a rotor region surface cut therein. In addition, there is provided a permanent magnet arrangement coupled by an adhesive to the rotor region of the rotor shaft for facilitating conversion of electromagnetic energy to mechanical energy. The adhesion between the permanent magnet arrangement and the rotor region surface is enhanced by the rotor region surface cut.
As noted, the rotor region surface cut is a continuation of a working surface region cut, the working region of the rotor shaft having a threaded potion. As such, therefore, the working region surface cut is a first cut pass of the threaded portion of the working region of the rotor shaft.
In accordance with a process aspect of the invention, a rotor shaft for a permanent magnet motor formed by the process of:
first preparing a working surface region of a precision shaft using a cutting tool, the step of first preparing including the further step of performing a first cutting pass by the cutting tool;
second preparing a rotor surface region of the precision shaft using the cutting tool, the rotor surface region having a first predetermined cross-sectional diameter, the step of second preparing including the step of continuing a first cutting pass by the cutting tool into the rotor surface region of the precision shaft, the step of continuing a first cutting pass by the cutting tool forming a continuous helical cut along the working and rotor surface regions of the precision shaft, whereby an inter-helical cut region of the rotor surface region of the precision shaft retains the first predetermined cross-sectional diameter;
preparing the working region of the precision shaft using the cutting tool, the step of third preparing including at least a second cutting pass by the cutting tool into the working surface region of the precision shaft; and
installing a permanent magnet onto the rotor surface region of the precision shaft by use of an adhesive, whereby the installed permanent magnet on the rotor surface region of the precision shaft forms the rotor shaft of the permanent magnet motor.